The invention generally relates to determining technique and system for deriving a time lapse low frequency model using both seismic data and a flow simulation model.
Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A survey typically involves deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, changing their direction of propagation and other properties. Part of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposits.
Some surveys are known as “marine” surveys because they are conducted in marine environments. However, “marine” surveys may be conducted not only in saltwater environments, but also in fresh and brackish waters. In one type of marine survey, called a “towed-array” survey, an array of seismic sensor-containing streamers and sources is towed behind a survey vessel.
For purposes of observing changes in a producing field over time, a series of towed seismic surveys of the producing field, separated by months or years, may be conducted. Thus, an initial survey (called “a base survey”) may be conducted before or after the well completion equipment is installed, and thereafter, subsequent surveys (called “monitor,” or “repeat surveys”) are conducted for purposes of observing changes in the producing field. Ideally, the only change between any two of the surveys should be in the fluids (i.e., oil, gas and/or water) that are produced or displaced from the producing field. In time lapse analysis, also called “4-D analysis,” differences are taken between the surveys to ideally reveal only the changes in the produced/displaced fluids, with the geology (ideally being the same for each survey) canceling out.